Amplitude refers to the maximum angle of oscillation of a watch's balance wheel, which is crucial for maintaining accurate timekeeping.
Amplitude is the angle of arc through which the balance wheel swings during each oscillation, measured in degrees. A fully wound watch typically shows 270-310 degrees of amplitude. Adequate amplitude ensures the escapement functions correctly—too low (under 180 degrees) risks the watch stopping or running erratically; too high can cause over-banking where the pallet fork hits the banking pins.
Low amplitude typically indicates insufficient power delivery—often from a nearly depleted mainspring, dried lubricants creating friction, worn pivot holes, or a damaged escapement. It matters because amplitude below 200 degrees causes unreliable escapement engagement, leading to inaccuracy or stopping. A watchmaker checks amplitude using a timegrapher during service, with readings below 220 degrees warranting investigation.
Amplitude varies between positions—crown up, crown down, dial up, dial down—typically by 20-40 degrees in a well-regulated watch. Significant variation (50+ degrees between positions) indicates pivot wear, lubrication issues, or an out-of-poise balance wheel. Professional regulation involves measuring amplitude in all six positions and adjusting to achieve consistent timekeeping across orientations.